They clear some of the main hazards (12)
I believe the answer is:
minesweepers
'the main hazards' is the definition.
The answer and definition can be both man-made objects as well as being plural nouns.
Maybe you can see a link between them that I can't see?
'they clear some' is the wordplay.
I cannot quite understand how this works, but
'clear' could be 'sweep' (I've seen this before) and 'sweep' is found in the answer.
This may be the basis of clue (or it may be nonsense).
'of' is the link.
Can you help me to learn more?
(Another definition for minesweepers that I've seen is " Types of war vessels".)